Surface emitting semiconductor laser, and method and apparatus for fabricating the same

ABSTRACT

A method of fabricating a surface emitting semiconductor laser includes a first step of forming, on a substrate, multiple monitor-use semiconductor layers having stripes radiating from a center of the substrate, and a laser portion that includes semiconductor layers and is located on the periphery of the multiple monitor-use semiconductor layers, a second step of monitoring oxidized conditions on the multiple monitor-use semiconductor layers when a selectively oxidized region is formed in the laser portion, and a third step of controlling oxidization of the selectively oxidized region on the basis of the oxidized conditions thus monitored.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a surface emitting semiconductorlaser used as a source for optical information processing, opticalcommunications, optical recording and image forming. The presentinvention also relates to a method and apparatus for fabricating such asurface emitting semiconductor laser. More particularly, the presentinvention relates to a technique of accurately defining an aperturesurrounded by a selectively oxidized portion of a current confinementregion.

[0003] 2. Description of the Related Art

[0004] Recently, there has been an increased demand for a surfaceemitting semiconductor laser capable of easily realizing an array ofsources in the technical fields of optical communications and opticalinterconnections. Such a laser is also called vertical-cavitysurface-emitting laser diode (VCSEL).

[0005] The surface emitting semiconductor laser is categorized into aproton injection type with a gain waveguide structure, and a selectiveoxidization type with a refractive ratio waveguide structure. Nowadays,the latter is getting the mainstream. Generally, the selectiveoxidization type semiconductor laser has a laser portion of a mesastructure (laser-use mesa). A current narrowing or confining regionformed by a selectively oxidizing part of an AlAs layer or AlGaAs layeris formed in the vicinity of the active region of the mesa. The currentconfinement layer has an increased resistivity and a reduced refractiveindex. This results in an optical waveguide path.

[0006] The degree of dimensional accuracy of the non-oxidized regionsurrounded by an aperture formed in the current confinement layer anddefined by the selectively oxidized region is a very important factorthat determines the device performance. The threshold current of laserand the transverse oscillation mode greatly depend on the diameter ofthe aperture.

[0007] A proposal to solve the above problems is described in JapaneseUnexamined Patent Publication No. 2001-93897. The proposal forms alinear stripe pattern that is formed on a substrate and has the samecomposition as that of a pattern of the laser portion having a mesashape formed on the same substrate. The linear stripe pattern is used asa sample for monitoring. In an oxidization step, the degree of advanceof the oxidization reaction on the monitor sample is monitored, andoxidization of the laser portion is controlled based on the monitoreddegree of advance. The proposal utilizes a phenomenon such that thereflectance of an AlAs layer in the monitor sample becomes higher asoxidization thereof advances. Light is projected onto the stripe-likemonitor sample, and the reflectance thereof is monitored.

[0008]FIG. 13 is a graph of a relation between light projected onto thestripe-like monitor sample and its reflectance, and FIG. 14 is a graphof a method for controlling oxidization using the conventional monitorsample. Light of a selected wavelength is extracted from the lightprojected onto the monitor sample, and reflected light is monitored. Asshown in FIG. 14, an AlAs layer of the monitor sample has reflectancevalues r1 and r2 when oxidization thereof starts (time t1) and ends(time t2), respectively. Oxidization of the current confinement layer iscontrolled by detecting the reflectance obtained at times t1 and t2 orits variation.

[0009] However, the proposal described in the above-mentionedpublication has the following problems to be solved. The monitor-usesample has a width narrower than the diameter of the mesa of the laserportion (the outside diameter for a cylindrically-shaped mesa) and astripe-like pattern formed on the substrate on which stripe lines arearranged with a constant period. The monitor sample is defined byanisotropic etching so that it can be simultaneously formed with themesa of the laser portion. However, the monitor samples of laser deviceshave considerable dispersion of the line width due to the actual etchingconditions. Sometimes, the sidewall (stripe edge) of the monitor sampleis not vertical but inclined. When these faulty monitoring samples aresubject to oxidization, optical diffraction may take place and preventaccurate measurement of variation from the reflectance r1.

[0010]FIG. 15 shows a graph of a relation between reflectance vs.oxidization time for the monitor sample. It is difficult to accuratelyidentify the oxidization initiating time (circle of broken line in FIG.15) from variation in the reflectance. Further, there is a dispersion ofthe stripe line width. Thus, the average reflectance r1 obtained fromthe stripe pattern fluctuates. This makes it difficult to accuratelymeasure the reflectance r1 and detect the oxidization initiating timet1.

[0011] If tracking of the oxidized condition on the monitor sampleincludes error, it will be difficult to reproduce the aperture in thecurrent confinement region as designed at the time of stopping theoxidization reaction. This degrades the production yield and preventscost reduction. There is another disadvantage. After the step ofoxidizing the current oxidization layer, an insulation film and a metalelectrode are photolithographically formed. In these processes, theresist films may not be deposited on the substrate evenly. Resist isdropped on the substrate that is being rotated, the stripe patternrestricts movement of the resist and prevents the resist from smoothlymoving towards the ends from the center of the substrate. This mayprevent evenness in the film thickness of resist. The unevennessdegrades the accuracy of an outgoing aperture formed in the metalelectrode and affects alignment of the outgoing window with the aperturein the current confinement layer and the optical axis of the laserportion.

SUMMARY OF THE INVENTION

[0012] The present invention has been made in view of the abovecircumstances and provides a surface emitting semiconductor laser and amethod of fabricating the same.

[0013] According to an aspect of the present invention, a method offabricating a surface emitting semiconductor laser has the steps of:forming a laser portion of semiconductor layers and at least two kindsof monitor-use semiconductor layers on a substrate, the laser portionincluding a first reflection mirror layer of a first conduction type, anactive region, a III-V semiconductor layer containing Al and a secondreflection mirror of a second conduction type, the at least two kinds ofmonitor-use semiconductor layers having oxidizable regions havingdifferent shapes; etching the laser portion so as to form a mesa on thesubstrate in which a side surface of the III-V semiconductor layercontained in the laser portion is exposed; starting oxidization of theIII-V semiconductor layer from the side surface; monitoring areflectance of each of the oxidizable regions of the at least two kindsof monitor-use semiconductor layers or its variation and obtaining, fromresults of monitoring, an oxidization terminating time at whichoxidization of the III-V semiconductor layer in the laser portion shouldbe terminated; and terminating oxidization of the III-V semiconductorlayer at the oxidization terminating time to thus define an aperturethat is a non-oxidized region of the III-V semiconductor layer.

[0014] According to another aspect of the present invention, a method offabricating a surface emitting semiconductor laser includes the stepsof: forming a laminate of semiconductor layers including a III-Vsemiconductor layer containing Al on a substrate; forming, from thelaminate, first, second and third mesas of different sizes on thesubstrate so that side surfaces of III-V semiconductor layers includedin the first through third mesas are exposed; oxidizing the III-Vsemiconductor layers of the first through third mesas from the sidesurfaces thereof; optically monitoring oxidized conditions on the III-Vsemiconductor layers of the second and third mesas and obtaining, fromtimes when the III-V semiconductor layers of the second and third mesasare terminated as well as the sizes thereof, an oxidization terminatingtime when oxidization of the III-V semiconductor layer of the first mesashould be terminated; and terminating oxidization of the III-Vsemiconductor layer of the first mesa to thus form a current confinementlayer including an aperture that is a non-oxidized region of the III-Vsemiconductor layer of the first mesa.

[0015] According to yet another aspect of the present invention, amethod of fabricating a surface emitting semiconductor laser includesthe steps of: forming, on a substrate, multiple monitor-usesemiconductor layers having stripes radiating from a center of thesubstrate, and a laser portion that includes semiconductor layers and islocated on the periphery of the multiple monitor-use semiconductorlayers; monitoring oxidized conditions on the multiple monitor-usesemiconductor layers when a selectively oxidized region is formed in thelaser portion; and controlling oxidization of the selectively oxidizedregion on the basis of the oxidized conditions thus monitored.

[0016] According to a further aspect of the present invention, a methodof fabricating a surface emitting semiconductor laser includes the stepsof: forming, on a substrate, multiple monitor-use semiconductor layershaving stripes radiating towards ends of the substrate, and a laserportion that includes semiconductor layers and is located adjacent tothe multiple monitor-use semiconductor layers; monitoring oxidizedconditions on the multiple monitor-use semiconductor layers when aselectively oxidized region is formed in the laser portion; andcontrolling oxidization of the selectively oxidized region on the basisof the oxidized conditions thus monitored.

[0017] According to a still further aspect of the present invention, asurface emitting semiconductor laser includes: a substrate; and alaminate of semiconductor layers on the substrate, the semiconductorlayers including a first reflection mirror of a first conduction type,an active region on the first reflector mirror, a current confinementregion including an oxidized region, and a second reflection mirror of asecond conduction type, a mesa ranging at least from the secondreflection mirror to the current confinement layer, the mesa extendingat least from the second reflection mirror to the current confinementlayer, the oxidized region of the current confinement layer utilizing anoxidization terminating time obtained by detecting times when oxidizableregions included in at least two kinds of monitor-use semiconductorlayers having different shapes are totally oxidized.

[0018] According to another aspect of the present invention, anapparatus for fabricating a surface emitting semiconductor laserincludes: a projection part projecting light onto an area including atleast two kinds of monitor-use mesas respectively including III-Vsemiconductor layers that contain Al and have side surfaces exposed,when the side surfaces and a side surface of a III-V semiconductor layerof a laser-use mesa that contains Al and a side surface exposed areoxidized; a photoelectric conversion part converting reflected lightsfrom the monitor-use mesas into electrical signals; an oxidizationterminating time estimation part that detects times when the III-Vsemiconductor layers of the two kinds of monitor-use mesas are totallyoxidized on the basis of the electrical signals, and estimates anoxidization terminating time when oxidization of the III-V semiconductorlayer of the laser-use mesa should be terminated; and an oxidizationcontrol part causing oxidization of the III-V semiconductor layer of thelaser-use mesa to be terminated at the oxidization terminating time tothus define a current confinement layer in the laser-use mesa.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Preferred embodiments of the present invention will be describedin detail based on the following figures, wherein:

[0020]FIG. 1A is a cross-sectional view of a surface emittingsemiconductor device according to a first embodiment of the presentinvention, wherein the cross-sectional view is taken along a line X-Xshown in FIG. 1B;

[0021]FIG. 1B is a plan view of the surface emitting semiconductor lasershown in FIG. 1A;

[0022]FIGS. 2A, 2B and 2C are cross-sectional views of steps of a methodof fabricating the surface emitting semiconductor laser shown in FIGS.1A and 1B;

[0023]FIGS. 3A, 3B and 3C are cross-sectional views of steps of a methodof fabricating the surface emitting semiconductor laser shown in FIGS.1A and 1B;

[0024]FIG. 4 illustrates oxidized conditions on an AlAs layer of alaser-use mesa and oxidized conditions of an AlAs layer of a monitor-usemesa;

[0025]FIG. 5 is a graph of a relation between an average reflectanceinvolved in a monitor-use stripe pattern and oxidization time;

[0026]FIG. 6 is a block diagram of an oxidization control apparatusaccording to an embodiment of the present invention;

[0027]FIG. 7 is a graph illustrating an average reflectance vs.oxidization time characteristic measured when two kinds of monitor-usemesas are used;

[0028]FIG. 8A is a graph showing accuracy of oxidization distance d3obtained when two kinds of monitor-use mesas according to an embodimentof the present invention are used;

[0029]FIG. 8B is a graph showing accuracy of oxidization distanceobtained when a single kind of monitor-use mesa is used;

[0030]FIGS. 9A and 9B are respectively plan views of variations of thetwo kinds of monitor-use mesas;

[0031]FIGS. 10A and 10B are respectively plan views of radiating stripepatterns according to a second embodiment of the present invention;

[0032]FIGS. 11A and 11B are plan views of variations of the radiatingstripe patterns shown in FIGS. 10A and 10B;

[0033]FIGS. 12A, 12B and 12C are plan views of other variations of theradiating stripe patterns shown in FIGS. 10A and 10B;

[0034]FIG. 13 is a graph showing a relation between the wavelength oflight projected onto a conventional monitor-use sample and reflectance;

[0035]FIG. 14 is a graph showing an oxidization control method that iscarried out when the conventional monitor-use sample is used; and

[0036]FIG. 15 is a graph showing a relation between the reflectance andoxidization time obtained when the conventional monitor-use sample isused.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] A description will now be given of embodiments of the presentinvention with reference to the accompanying drawings.

[0038]FIG. 1A is a cross-sectional view of a surface emittingsemiconductor laser according to a first embodiment of the presentinvention, and FIG. 1B is a plan view thereof. The present embodiment isa selective oxidization type surface emitting semiconductor laser 100equipped with a laser portion 101 having a cylindrical mesa structure(post structure or pillar structure). A protection film that covers thelaser portion (mesa) 101 and a bonding pad portion that extends from ametal contact layer are omitted from illustration for the sake ofsimplicity.

[0039] The laser 100 has an n-type GaAs substrate 1, on which an n-typebuffer layer 2 is provided. An n-type lower DBR (Distributed BraggReflector) 3 is provided on the buffer layer 2. On the lower DBR 3,laminated are an undoped lower spacer layer 4, an undoped quantum wellactive layer 5, and an undoped upper spacer layer 6 in this order. Anactive region 7 is formed so as to include the layers 4, 5 and 6. Ap-type upper DBR 8 and a p-type contact layer 9 are laminated on theactive region 7 in this order. The lowermost layer of the upper DBR 8 isa p-type AlAs layer 10, which serves as a current confinement layerequipped with a circular aperture 21 surrounded by an oxidized region.

[0040] A contact layer 9 is formed on the upper DBR 8. An interlayerinsulation film 12 covers the bottom and side surfaces of the mesa aswell as part of the top surface thereof. A metal layer 13 is formed onthe interlayer insulation film 12. The metal layer 13 makes an ohmiccontact with the contact layer 9, and serves as a p-side electrode forinjecting current to the laser portion. An n-type backside electrode 14is provided on the back surface of the substrate 1. A circular apertureis formed in the metal layer 13 so as to be located in the centerthereof. This aperture serves as an outgoing window 11 via which laseris emitted outwards. The center of the outgoing window 11 is alignedwith the aperture of the current confinement layer 10, and substantiallycoincides with the optical axis that extends from the substratevertically and passes through the center of the laser portion 101.

[0041] The lower DBR 3 is a multiple laminate of n-typeAl_(0.9)Ga_(0.1)As layers and Al_(0.3)Ga_(0.7)As layers, each of whichhas a thickness λ/4n_(r) where X is the oscillation wavelength and n_(r)is the refractive index of the medium. The paired layers havingdifferent composition ratios are alternately laminated to a thickness of40.5 periods. The carrier concentration of the lower DBR 3 is 3×10¹⁸cm⁻³ after silicon that is an n-type impurity is doped.

[0042] In the active region 7, the lower spacer layer 4 is an undopedAl_(0.6)Ga_(0.4)As layer. The quantum well active layer 5 includes anundoped Al_(0.11)Ga_(0.89)As quantum well layer and an undopedAl_(0.3)Ga_(0.7)As barrier layer. The upper spacer layer 6 is an undopedAl_(0.6)Ga_(0.4)As layer.

[0043] The upper DBR 8 is a multiple laminate of p-typeAl_(0.9)Ga_(0.1)As layer and p-type Al_(0.3)Ga_(0.7)As layers, eachhaving a thickness λ/4n_(r) where λ is the oscillation wavelength andn_(r) is the refractive index of the medium. The paired layers havingdifferent composition ratios are alternately laminated to a thickness of30 periods. The carrier concentration of the upper DBR 8 is 3×10¹⁸ cm⁻³after carbon that is a p-type impurity is doped.

[0044] The p-type contact layer 9 is a GaAs layer and is 20 nm thick.The carrier concentration of the p-type contact layer 9 is 1×10²⁰ cm⁻³after carbon that is a p-type impurity is doped. The metal layer 13,which serves as the p-side electrode, is a laminate of Ti/Au.

[0045] Although not shown in FIGS. 1A and 1B, in order to reduce theseries resistance of the laser portion, practically, an intermediate(graded) layer having an intermediate mixed crystal ratio of GaAs/AlAsbetween the p-type Al_(0.9)Ga_(0.1)As layer and the p-typeAl_(0.3)Ga_(0.7)As layer may be provided on the upper DBR 8 or below thelower DBR 3.

[0046] A description will now be given of a method of fabricating thesurface emitting semiconductor laser shown in FIGS. 1A and 1B. In thepresent embodiment, a monitor-use stripe pattern having semiconductorlayers is formed in the center of the substrate 1, and semiconductorlayers for laser portions are arranged around its periphery. In thefigures described blow, physical relations mentioned above are omitted,and a process for simultaneously forming semiconductor layers for laserportions and monitor-use semiconductor layers on the substrate 1 areschematically illustrated.

[0047] As shown in FIG. 2A, the buffer layer 2, the lower DBR 3, theactive region 7, the upper DBR 8 and the contact layer 9 are laminatedon the substrate 1 in this order. As shown in FIG. 2B, silicon oxidelayers 201, 201 a and 201 b are formed on the contact layer 9 bypatterning. The silicon oxide layer 201 is a mask layer for forming themesa of the laser portion 101. The silicon oxide layers 201 a and 201 bare mask layers for forming mesas that are semiconductor layers for usein monitoring. The mesa of the laser portion 101 is a cylindricalpillar, while the monitor-use semiconductor layers are like a slenderstripe. The silicon oxide layer 201 is shaped into a circular pattern,and the silicon oxide layers 201 a and 201 b are shaped into slenderpatterns. The cross section of FIG. 2B shows the short-side widths ofthe silicon oxide layers 201 a and 201 b, wherein the short-side widthof the silicon oxide layer 201 b is shorter than that of the siliconoxide width 201 a. The widths of the silicon oxide layers 201 a and 201b are shorter than the diameter of the silicon oxide layer 201.

[0048] As shown in FIG. 2C, a laminate ranging from the contact layer 9,the upper DBR 8, the active region 8 and part of the lower DBR 3 isanisotropically etched by reactive ion etching (RIE) with a mixed gas ofboron trichloride and chlorine (BCl₃ and Cl₂). This anisotropic etchinguses the silicon oxide films 201, 201 a and 201 b as masks, and definesa laser-use mesa 210 and monitor-use mesas 210 a and 210 b. It is notnecessarily required to cause etching to advance up to the lower DBR 3but to expose at least the side surface of the AlAs layer 10. Forexample, etching of up to the active layer 5 of the active region 7 maybe accepted.

[0049] The mesa 210 of the laser portion 101 is like a cylindricalpillar, and the monitor-use mesas 210 a and 210 b are like slenderrectangular parallelepipeds. The long-side widths of the mesas 210 a and201 b are much longer than the short-side widths thereof. The two mesas210 a and 210 b having the different widths are paired, and multiplepairs of mesas are arranged at given pitches in the center of thesubstrate 1 so as to form straight stripes.

[0050] Next, oxidization of the AlAs layer (current confinement layer)10 of the mesa 210 is started (FIG. 3A). This oxidization uses wetoxidization in which a water vapor obtained by bubbling pure waterheated to 95° C. is transported to a wet oxidization chamber withnitrogen being used as carrier gas. The substrate is put in theoxidization chamber in advance and the in-chamber temperature is set atapproximately 340° C. The AlAs layers included in the mesas 210 and 210a and 210 b are oxidized from the side surfaces thereof.

[0051] In the present embodiment, in order to control the oxidizationreaction on the AlAs layer 10, namely, the size of the aperture 21thereof, oxidized conditions of the AlAs layers 10 a and 10 b of themesas 210 a and 210 b are monitored, and the terminating time ofoxidization of the AlAs layer 10 is estimated on the basis of theoxidized conditions of the AlAs layers 10 a and 10 b. This control maybe accomplished by an oxidization control apparatus 600 shown in FIG. 6.The apparatus 600 includes a lamp 601, a spectroscope 602, aphotodetector 603, and a control unit 604. The lamp 601 projects lightin the wavelength range of 400-1100 nm onto the area including thestripe pattern of the mesas 210 a and 210 b on the substrate 1. Thespectroscope 602 optically splits reflected light from the stripepattern into given wavelengths. The photodetector 603 is alight-receiving element such as a photodiode, and converts split lightsinto electrical signals. The control unit 604 monitors the signals fromthe photodetector 603, and controls oxidization of the AlAs layer of themesa 210.

[0052] When AlAs (or AlGaAs) is oxidized, AlO_(x) is formed in theoxidized portion, which is an insulator, and has a reflectance differentfrom that of AlAs. For instance, the average reflectance in thewavelength range of 800-1000 nm is 0.45 for AlAs and is 0.58 forAlO_(x). Thus, by measuring the average reflectance of the AlAs layer inprogress of oxidization, it is possible to track the degree of progressof oxidization reaction on the AlAs layer.

[0053]FIG. 4 shows various oxidized conditions of the AlAs layer 10 ofthe mesa 210 that forms the laser portion 101, and various oxidizedconditions of the AlAs layers 10 a and 10 b of the monitor-use mesas 210a and 210 b. FIG. 5 is a graph of an average reflectance vs. oxidizationtime characteristic of a stripe pattern for use in monitoring.

[0054] The planer pattern (oxidizable region) of the AlAs layer 10 ofthe mesa 210 for the laser portion 101 has a circular shape, and has adiameter D prior to oxidization. The planer pattern (oxidizable region)of the AlAs layer 10 a of the monitor-use mesa 210 a has a width W2 onthe short side and a height (length) H on the long side. Similarly, theplaner pattern of the AlAs layer 10 b of the monitor-use mesa 210 b hasa width W1 on the short side and the same height (length) H on the longside as that of the monitor-use mesa 210 a. These patterns have arelation such that W1<W2<D, W1<<H, and W2<<H.

[0055] In FIGS. 4 and 5, at the oxidization starting time TO,oxidization of the AlAs layers 10, 10 a and 10 b of the mesas 210, 210 aand 210 b has not yet been started, and the average reflectance from thestripe pattern is at an initial value RO. The planer patterns of theAlAs layers 10, 10 a and 10 b are shown as blank areas in FIG. 4. Afteroxidization starts, oxidization of the AlAs layer 10 of the mesa 210evenly advances inwards from its side surface. In FIG. 4, oxidized areasare illustrated with hatching. Simultaneously, oxidization of the AlAslayers 10 a and 10 b of the mesas 210 a and 210 b evenly advancesinwards from the side surfaces thereof. Since the heights H of themonitor-use mesas 210 a and 210 b are much longer than the widths W1 andW2, it can be considered that oxidization of the AlAs layers 10 a and 10b advances from the opposing long sides H of the mesas 210 a and 210 b.

[0056] The AlAs layers 10, 10 a and 10 b are oxidized at the same rateof oxidization from time TO. When the oxidizable region of the AlAslayer 10 b of the mesa 210 b is totally oxidized, in other words, whenthe width W2 of the mesa 210 b is totally oxidized, a unique waveformthat reflects the ratio of variation of the reflectance from the stripepattern for monitoring is observed. Oxidization of the mesa 210 b doesnot advance any more. This results in a turning point R1 at whichinclination of the average reflectance becomes small. The turning pointR1 takes place at time T1. At time T1, oxidization of the AlAs layer 10a of the mesa 210 a has advanced for a distance of W1/2 from theopposing sides, and a non-oxidized region (W2−W1) remains in the centerthereof. In FIG. 4, the region that has been oxidized is illustrated asa hatched area, and the non-oxidized region is illustrated as a blankarea. Oxidization of the mesa 210 of the laser portion 101 has advancedfor a distance of W1/2 from the sidewall thereof, and a non-oxidizedregion of an aperture D1 (=D−W1) remains in the center thereof.

[0057] When the AlAs layer 10 a of the mesa 210 a is totally oxidized, aturning point R2 takes place at which the inclination of the averagereflectance from the stripe pattern of the monitor-use mesa 210 afurther changes. This is because oxidization of the mesa 210 a iscompleted and does not advance any more. The turning point R2 takesplace at oxidization time T2. At time T2, oxidization of the mesa 210 ofthe laser portion 101 has advanced for a distance of oxidizationdistance W2/2 from the sidewall thereof, and a non-oxidized region of anaperture D2 (=D−W2) remains at the center.

[0058] According to an aspect of the present invention, oxidizationterminating time T3 for forming designed oxidization distance d3(namely, an aperture having diameter D3) in the AlAs layer 10 on thebasis of the times T1 and T2 at which the turning points R1 and R2 ofthe average reflectance are obtained.

[0059] The widths W1 and W2 of the mesas 210 a and 210 b for use inmonitoring are known, and the times T1 and T2 can be obtained from theturning points R1 and R2. Thus, it can be seen that oxidization advancesfor a distance Δd=(W2−W1)/2 during a time ΔT=T2−T1. It will be notedthat “½” is provided taking into consideration that oxidizationsimultaneously advances from the both sides of each mesa. The rate ofoxidization of the AlAs layer can be obtained from the time ΔT andoxidization distance Δd. From the above relation, time T3 at whichoxidization advances to the designed oxidization distance d3 can beobtained as follows:

T3=T2+ΔT/Δd(d3−W2/2).

[0060] By terminating the oxidization process when time T3 elapses, itis possible to form the aperture 21 having the designed oxidizationdistance d3 or dimensional accuracy D3 in the mesa 210 on the laserportion 101. The above-mentioned oxidization control process is carriedout by the control apparatus 604, and is preferably programmed in theform of software stored therein.

[0061] After the oxidization process, as shown in FIG. 3A, part of theAlAs layer 10 of the mesa 210 is selectively oxidized, and the aperture21 is formed in the center of the current confinement layer 10.

[0062] Turning to FIG. 3B, the silicon oxide layers 201, 201 a and 201 bused as the etching masks are removed, and the interlayer insulationfilm 12 is formed so as to form the mesa 210. Of course, it is notnecessary to apply subsequent processes to the monitor-use mesas 210 aand 201 b in the same manner as the mesa 210.

[0063] Then, the aperture 12 a is formed in the interlayer insulationfilm 12 on the top of the mesa 210, and the metal layer 13 is providedthereon. An aperture serving as the outgoing window 11 is formed in thecenter of the metal layer 13, and the n-side backside electrode 14 isformed on the back surface of the substrate 1.

[0064] According to the present embodiment, two kinds of mesa-likesemiconductor layers having different widths (W1, W2) are provided foruse in monitoring oxidization, and attention is paid to unique wave formchanges of the reflectance when the mesas 210 a and 210 b have beentotally oxidized. The detection of the unit waveform change makes itpossible to accurately monitor and track the progress of oxidization onthe monitor-use mesas.

[0065]FIG. 7 shows measurement results obtained when the two kinds ofmonitor-use mesas are actually employed. The two kinds of mesas thatform stripe patterns having widths W1 of 9 um and 18 um, respectively,and are subject to an oxidization control in which the oxidizationtemperature is set at 370° C. and the oxidization distance d3 is setequal to 11 μm. The two different mesas form a pattern of a pair ofstripes. Multiple pairs of stripes are disposed in the center of thesubstrate 1. The aforementioned oxidization control apparatus 600initiates the oxidization process for the substrate 1, and commences toproject white light from the lamp 601 onto the area including the pairsof stripes arranged in the center of the substrate 1. Reflected lightfrom the substrate 1 is split into lights of the given wavelengths bythe spectroscope 602, which lights are then monitored.

[0066] In FIG. 7, the vertical axis denotes the reflectance, and thehorizontal axis denotes the oxidization time. The reflectance of thevertical axis may be replaced with the output of an equivalentelectrical signal obtained by photoelectric conversion of a selected oneof the split lights. It can be seen from FIG. 7 that the first explicitchange of the reflectance after initiation of oxidization takes placewhen the monitor-use mesa having the comparatively small width W1 (equalto 9 μm) has just been oxidized totally (time T1), and that the secondexplicit change of the reflection occurs when the other monitor-use mesahaving the comparatively large width W2 (equal to 18 μm) has just beenoxidized totally (time T2).

[0067] It is possible to determine which one of the split lights orwavelengths from the spectroscope 602 should be selected to monitor thereflectance of its change by taking into account the patterns, sizes andlaminate structures of the monitor-use mesas or oxidization environment.Preferably, one of the split lights or wavelengths that exhibitsremarkable change in the reflectance should be selected.

[0068]FIG. 8A shows the accuracy of the oxidization distance d3 obtainedwhen the two kinds of monitor-use mesas according to the presentembodiment are used, and FIG. 8B shows the accuracy of the oxidizationdistance obtained when only one monitor-use mesa is used. The horizontalaxes of FIGS. 8A and 8B denote the lot numbers of substrates subject toa batch process, and the vertical axes thereof denote normalizedoxidization depths formed in the mesa 210. As is seen from FIG. 8A, theoxidization distance formed in the mesa 210 is regulated within a rangeof about 2%, and the standard deviation p is equal to 0.99%. Incontrast, in the conventional oxidization control shown in FIG. 8B, theoxidization distance (which corresponds to the oxidization distance d3)is regulated within a broader range of about 5%, and the standarddeviation p is equal to 2.35%. It can be seen from the above that theuse of the two kinds of monitor-use mesas for estimating the oxidizationdistance d3 from the respective oxidization terminating times makes itpossible to more accurately control the oxidization distance d3 or theaperture D3 In the present embodiment, the stripes of the two kinds ofmesas or semiconductor layers for monitoring are formed on the substrate(or wafer) separate from the laser portion 101. Instead of theabove-mentioned stripes, it is possible to employ stripes respectivelyformed by cylindrical mesas. For example, the mesas 210 a and 210 b foruse in monitoring may be structured so that the AlAs layers 10 a and 10b have an oval, ellipse or polygonal planer shape. Similarly, the mesaof the laser portion 101 is not limited to the cylindrical post, but maybe a square or rectangular post. The present invention does notnecessarily need the straight stripes, but any pattern formed by a pairof stripes of the mesas 210 a and 210 b may be used.

[0069]FIGS. 9A and 9B respectively show variations of the monitor-usemesas. The two kinds of mesas for use in monitoring do not essentiallyrequire physical separation. For instance, as shown in FIG. 9A, a mesa220 for monitoring has a pattern having regions of widths W1 and W2. Itis also possible to interpose another mesa 221 having the same patternas that of the mesa 220 between integrally formed stripes of the mesa220 so that the widths W1 and W2 of the mesa 220 face the widths W2 andW1 of the mesa 221, respectively. As shown in FIG. 9B, mesas 231 and 232for monitoring are alternately arranged. As described above, even whenthe mesas have the same pattern, these mesas can be arranged so as tosubstantially have two kinds of mesas for use in monitoring. In short,it is enough to have at least two kinds of oxidization regions havingdifferent widths, sizes or dimensions.

Second Embodiment

[0070] A description will now be given of a second embodiment of thepresent invention. In the foregoing, the monitor-use mesas are arrangedso as to form a stripe pattern in the center of the substrate. Incontrast, according to the second embodiment of the present invention, astripe pattern 701 that has stripes radiating from the center of thesubstrate 1 is used, as shown in FIG. 10A. The radial stripe pattern 701includes multiple pairs of mesas, each pair having two kinds of mesashaving different widths W1 and W2 as in the case of the firstembodiment. Multiple mesas 702 that respectively form laser portions arearranged around the stripe pattern 701.

[0071] In the process following the formation of mesas, an etching maskof resist in the photolithographic process is used to define theaperture 12 a of the interlayer insulation film 12 and the outgoingwindow 11 of the metal layer 13. The process of forming the resistincludes spin coating in which resist is dropped towards the substrate 1that is rotating. In this spin coating, resist dropped on the substratemay move smoothly along the stripe pattern 701 of the stripes radiatingfrom the center of the substrate 1 and having symmetry with respect tothe center. It is therefore possible to deposit the resist having aneven film thickness over the substrate 1. By enhancing the accuracy ofthe resist mask, it is possible to improve the accuracy of positioningthe aperture 12 a and the outgoing window 11 and align them with theoptical axis of the laser portion 101.

[0072] The present invention is not limited to the two kinds of mesashaving different widths, but may use a monitor-use pattern of radialstrips each having the same width.

[0073]FIGS. 11A and 11B show modified examples of the monitor-use mesas.A radial stripe pattern 801 shown in FIG. 11A is a modification of theradial stripe pattern 701 shown in FIG. 10A. The radial pattern 801shown in FIG. 11A includes isolated patterns 801 a, each of which isinterposed between two stripes radiating from the center. The patterndensity on the outer side of the radial stripe pattern can be increasedby the isolated patterns 801 a. An increased pattern density on theouter side of the radial stripe pattern reduces the bottom areas of themesas, and light reflected from the stripe pattern includes reducedreflected light from the bottom areas of the mesas, so that noisecontained in the signal can be reduced and error in the reflectancemeasurement can be reduced.

[0074] A semi-radial stripe pattern 802 shown in FIG. 11B may be used.The semi-radial stripe pattern 802 has divided groups, each of which hasa center angle of 45° and includes a pattern of straight stripes. Thepatterns of straight stripes of the divided groups are arranged so as toform an angle of 45°. For example, a pattern 802 a includes straightstripes extending at an angle of 45° with respect to an orientation flat803 of the wafer or substrate, and a pattern 802 b includes straightstripes extending in parallel with the orientation flat 803. The dividedgroups are arranged so that the straight stripes of the adjacent groupsform an angle of 45° The semi-radial pattern 802 has reduced dispersionof the stripe width as compared to the radial pattern shown in FIG. 9A,and has an extremely increased pattern density as compared to the radialpattern shown in FIG. 8A.

[0075]FIGS. 12A through 12C respectively show variations of the radialstripe pattern. A pattern shown in FIG. 12A includes stripe patterns810, 811, 812 and 813, which are arranged on the substrate 1 withrotational symmetry. Each of the stripe patterns 810-813 includesstripes 810 a radiating from the center of the substrate 1 and stripes810 b extending in the direction perpendicular to the orientation flat803 of the substrate 1. A pattern shown in FIG. 12B includes fourright-angle patterns 820 with rotational symmetry. A pattern shown inFIG. 12C has four 45° inclined patterns 830 with rotational symmetry.Any of the patterns shown in FIGS. 12A through 12C bring about the sameeffects as the radial patterns. The straight stripes of the patterns 810b, 820 and 830 are not necessarily required to cross at the ends, butmay be spaced apart from each other at a given distance. The monitor-usemesas that form the patterns 810 b, 820 and 830 may be varied so as tohave pairs of mesas arranged at given intervals, each of which pairs hastwo kinds of mesas having different widths. It is also possible to forma stripe pattern with mesas each having the same width.

[0076] The present invention is not limited to the specificallydescribed embodiments, but other embodiments, variations andmodifications may be made without departing from the scope of theclaimed invention.

[0077] Besides the cylindrical mesa is used for the laser portion 101mentioned before, a mesa of a rectangular parallelepiped may be used.The monitor-used mesas are not limited to the stripe type but may haveany shape.

[0078] In the foregoing, the monitor-use mesas are used for controllingoxidization of the current confinement layer 10. However, oxidizationcontrol is not limited to the use of the monitor-use mesas. Forinstance, light may be projected onto the mesa surface of the laserportion 101, and the oxidized condition on the current confinement layer(AlAs layer) may be monitored directly for oxidization control.

[0079] Besides the current confinement layer 10 of AlAs, a III-Vsemiconductor containing Al, such as AlGaAs, may be used. In theforegoing, the upper DBR 8 is of p-type and the lower DBR 3 is of ntype. The above conduction types may be interchanged with each other. Ina case where the outgoing light is extracted from the backside of thesubstrate 1, the upper DBR 8 is designed to have a larger number oflayers than the lower DBR 3 and have a comparatively high reflectance.

[0080] The quantum well active layer is not limited to GaAs/AlGaAs-basedsemiconductors but may be made of, for example, GaAs/InGaAs-basedsemiconductors or GaAs/GaInNAs-based semiconductors. The emissionwavelength of light emitted from the quantum well layer is transparentto the GaAs substrate 1. This allows the outgoing light to be taken fromthe backside of the substrate 1 and brings about a process merit. In theforegoing, the contact layer 9 and the upper DBR 8 are handled asseparate layers in view of functions. However, the contact layer 9 ispart of the upper DBR 8.

[0081] In the foregoing, the n-side electrode 14 is formed on thebackside of the substrate 1. Alternatively, the n-type electrode may beprovided on the semiconductor layer (for instance, the lower DBR 3)exposed in the mesa bottom on the substrate.

[0082] Finally, the above description is summarized below.

[0083] According to an aspect of the present invention, the method offabricating a surface emitting semiconductor laser includes the stepsof: forming a laser portion of semiconductor layers and at least twokinds of monitor-use semiconductor layers on a substrate, the laserportion including a first reflection mirror layer of a first conductiontype, an active region, a III-V semiconductor layer containing Al and asecond reflection mirror of a second conduction type, the at least twokinds of monitor-use semiconductor layers having oxidizable regionshaving different shapes; etching the laser portion so as to form a mesaon the substrate in which a side surface of the III-V semiconductorlayer contained in the laser portion is exposed; starting oxidization ofthe III-V semiconductor layer from the side surface; monitoring areflectance of each of the oxidizable regions of the at least two kindsof monitor-use semiconductor layers or its variation and obtaining, fromresults of monitoring, an oxidization terminating time at whichoxidization of the III-V semiconductor layer in the laser portion shouldbe terminated; and terminating oxidization of the III-V semiconductorlayer at the oxidization terminating time to thus define an aperturethat is a non-oxidized region of the III-V semiconductor layer.

[0084] By using the two kinds of semiconductor layers having differentoxidizable regions, it becomes possible to accurately measure theturning points at which oxidization of the two kings of semiconductorlayers are respectively completed. It is further possible to obtaininformation about the oxidization times and oxidization distances of themonitor-use semiconductor layers. The information can be used toestimate the oxidization terminating time related to the aperture thatis to be formed in the III-V semiconductor layer of the laser portion.As a result, the aperture can be defined by highly reproducible processas designed.

[0085] Preferably, widths of the oxidizable regions of the at least twokinds of monitor-use semiconductor layers are smaller than a width of anoxidizable region of the III-V semiconductor layer of the laser portion,and the method further includes the steps of: obtaining a rate ofoxidization of the oxidizable regions of the monitor-use semiconductorlayers from variation in reflectance observed when the oxidizableregions of the monitor-use semiconductor layers are totally oxidized;and obtaining, from the rate of oxidization, a time when the aperturethat is the non-oxidized region of the laser portion should be formed.The reflectance of the monitor-use semiconductor layers or its variationappears explicitly. Therefore, the use of the reflectance or itsvariation contributes to detecting the oxidization rate more accuratelyand reducing error contained therein.

[0086] Preferably, the oxidizable regions of the at least two kinds ofmonitor-use semiconductor layers have widths W1 and W2 (W1<W2); thewidths W1 and W2 are smaller than a diameter D of the oxidizable regionof the III-V semiconductor layer of the laser portion; and the time whenthe aperture should be formed is obtained from the widths W1 and W2 andtimes T1 and T2 when the oxidizable regions of the at least two kinds ofmonitor-use semiconductor layers are totally oxidized. The relationbetween the oxidization time and rate can be obtained from themonitor-use semiconductor layers, so that the time necessary to definethe aperture of the non-oxidized region can be calculated byextrapolation.

[0087] Preferably, the at least two kinds of monitor-use semiconductorlayers have mesas that are formed by etching at the same time as themesa of the laser portion is formed; and the mesas of the at least twokinds of monitor-use semiconductor layers have a layer structureidentical to that of the mesa of the laser portion. Thus, theoxidization rates of the monitor-use semiconductor layers reflect theoxidization rate of the laser portion. Thus, monitoring the status ofadvancing oxidization of the monitor-use semiconductor layers isequivalent to that of the laser portion. It is therefore possible toaccurately control the oxidization reaction on the III-V semiconductorlayer containing Al.

[0088] Preferably, the at least two kinds of monitor-use semiconductorlayers are arranged so as to form a strip pattern on the substrate. Thisarrangement averages dispersion of the shapes of the semiconductorlayers and that of the oxidization distances, and realizes more reliablemonitoring of oxidization condition.

[0089] For example, the mesa of the laser portion has a post shape, andthe III-V semiconductor layer containing Al is one of an AlAs layer andan AlGaAs layer.

[0090] According to another aspect of the present invention, the methodof fabricating a surface emitting semiconductor laser includes the stepsof: forming a laminate of semiconductor layers including a III-Vsemiconductor layer containing Al on a substrate; forming, from thelaminate, first, second and third mesas of different sizes on thesubstrate so that side surfaces of III-V semiconductor layers includedin the first through third mesas are exposed; oxidizing the III-Vsemiconductor layers of the first through third mesas from the sidesurfaces thereof; optically monitoring oxidized conditions on the III-Vsemiconductor layers of the second and third mesas and obtaining, fromtimes when the III-V semiconductor layers of the second and third mesasare terminated as well as the sizes thereof, an oxidization terminatingtime when oxidization of the III-V semiconductor layer of the first mesashould be terminated; and terminating oxidization of the III-Vsemiconductor layer of the first mesa to thus form a current confinementlayer including an aperture that is a non-oxidized region of the III-Vsemiconductor layer of the first mesa.

[0091] Preferably, the first mesa has a post shape, and the non-oxidizedregion has a diameter of approximately 3 μm. Since the oxidizationterminating time can be estimated accurately, the non-oxidized region,namely, the aperture that is as small as approximately 3 μm can berealized. It is therefore possible to realize single-mode oscillation.

[0092] According to yet another aspect of the present invention, themethod of fabricating a surface emitting semiconductor laser includesthe steps of: forming, on a substrate, multiple monitor-usesemiconductor layers having stripes radiating from a center of thesubstrate, and a laser portion that includes semiconductor layers and islocated on the periphery of the multiple monitor-use semiconductorlayers; monitoring oxidized conditions on the multiple monitor-usesemiconductor layers when a selectively oxidized region is formed in thelaser portion; and controlling oxidization of the selectively oxidizedregion on the basis of the oxidized conditions thus monitored. Themonitor-use semiconductor layers radiate from the center of thesubstrate. This facilitates to smooth movement of resist that isspin-coated and achieves a uniform-thickness resist film.

[0093] Preferably, the stripes radiating from the center are arrangedwith rotational symmetry about the center. The stripes radiating fromthe center may be divided into multiple groups at a given center angle,and each of the multiple groups has straight stripes. The stripesincluded in the adjacent groups among the multiple groups may form anangle of approximately 45°. For example, the stripes are equally dividedinto eight multiple groups at an angle of 45°. The divided groups mayinclude straight stripes. The stripe pattern may be formed by a singlekind of monitor-use semiconductor layers, or multiple pairs of stripepattern, each being composed of two kinds of monitor-use semiconductorlayers.

[0094] According to a further aspect of the present invention, thesurface emitting semiconductor laser includes: a substrate; and alaminate of semiconductor layers on the substrate, the semiconductorlayers including a first reflection mirror of a first conduction type,an active region on the first reflector mirror, a current confinementregion including an oxidized region, and a second reflection mirror of asecond conduction type, a mesa ranging at least from the secondreflection mirror to the current confinement layer, the mesa extendingat least from the second reflection mirror to the current confinementlayer, the oxidized region of the current confinement layer utilizing anoxidization terminating time obtained by detecting times when oxidizableregions included in at least two kinds of monitor-use semiconductorlayers having different shapes are totally oxidized.

[0095] The above laser has the oxidized region of the currentconfinement layer with high dimensional accuracy. It is thereforepossible to efficiently confine current and light and to expect stableperformance as designed.

[0096] According to a still further aspect of the present invention, theapparatus for fabricating a surface emitting semiconductor laserincludes: a projection part projecting light onto an area including atleast two kinds of monitor-use mesas respectively including III-Vsemiconductor layers that contain Al and have side surfaces exposed,when the side surfaces and a side surface of a III-V semiconductor layerof a laser-use mesa that contains Al and a side surface exposed areoxidized; a photoelectric conversion part converting reflected lightsfrom the monitor-use mesas into electrical signals; an oxidizationterminating time estimation part that detects times when the III-Vsemiconductor layers of the two kinds of monitor-use mesas are totallyoxidized on the basis of the electrical signals, and estimates anoxidization terminating time when oxidization of the III-V semiconductorlayer of the laser-use mesa should be terminated; and an oxidizationcontrol part causing oxidization of the 111-V semiconductor layer of thelaser-use mesa to be terminated at the oxidization terminating time tothus define a current confinement layer in the laser-use mesa.

[0097] It is therefore possible to control the oxidized region of theIII-V semiconductor layer containing Al and realize highly reproducibleoxidized region with high dimensional accuracy. This achieves improvedproduction yield and cost reduction.

[0098] Although a few preferred embodiments of the present inventionhave been shown and described, it would be appreciated by those skilledin the art that changes may be made in these embodiments withoutdeparting from the principles and spirit of the invention, the scope ofwhich is defined in the claims and their equivalents.

What is claimed is:
 1. A method of fabricating a surface emittingsemiconductor laser comprising the steps of: forming a laser portion ofsemiconductor layers and at least two kinds of monitor-use semiconductorlayers on a substrate, the laser portion including a first reflectionmirror layer of a first conduction type, an active region, a III-Vsemiconductor layer containing Al and a second reflection mirror of asecond conduction type, the at least two kinds of monitor-usesemiconductor layers having oxidizable regions having different shapes;etching the laser portion so as to form a mesa on the substrate in whicha side surface of the III-V semiconductor layer contained in the laserportion is exposed; starting oxidization of the III-V semiconductorlayer from the side surface; monitoring a reflectance of each of theoxidizable regions of the at least two kinds of monitor-usesemiconductor layers or its variation and obtaining, from results ofmonitoring, an oxidization terminating time at which oxidization of theIII-V semiconductor layer in the laser portion should be terminated; andterminating oxidization of the III-V semiconductor layer at theoxidization terminating time to thus define an aperture that is anon-oxidized region of the III-V semiconductor layer.
 2. The method asclaimed in claim 1, wherein widths of the oxidizable regions of the atleast two kinds of monitor-use semiconductor layers are smaller than awidth of an oxidizable region of the III-V semiconductor layer of thelaser portion, the method further comprising the steps of: obtaining arate of oxidization of the oxidizable regions of the monitor-usesemiconductor layers from variation in reflectance observed when theoxidizable regions of the monitor-use semiconductor layers are totallyoxidized; and obtaining, from the rate of oxidization, a time when theaperture that is the non-oxidized region of the laser portion should beformed.
 3. The method as claimed in claim 1, wherein: the oxidizableregions of the at least two kinds of monitor-use semiconductor layershave widths W1 and W2 (W1<W2); the widths W1 and W2 are smaller than adiameter D of the oxidizable region of the III-V semiconductor layer ofthe laser portion; and the time when the aperture should be formed isobtained from the widths W1 and W2 and times T1 and T2 when theoxidizable regions of the at least two kinds of monitor-usesemiconductor layers are totally oxidized.
 4. The method as claimed inclaim 1, wherein: the at least two kinds of monitor-use semiconductorlayers have mesas that are formed by etching at the same time as themesa of the laser portion is formed; and the mesas of the at least twokinds of monitor-use semiconductor layers have a layer structureidentical to that of the mesa of the laser portion.
 5. The method asclaimed in claim 4, wherein the at least two kinds of monitor-usesemiconductor layers are arranged so as to form a strip pattern on thesubstrate.
 6. The method as claimed in claim 5, wherein the mesa of thelaser portion has a post shape, and the III-V semiconductor layercontaining Al is one of an AlAs layer and an AlGaAs layer.
 7. A methodof fabricating a surface emitting semiconductor laser comprising thesteps of: forming a laminate of semiconductor layers including a III-Vsemiconductor layer containing Al on a substrate; forming, from thelaminate, first, second and third mesas of different sizes on thesubstrate so that side surfaces of III-V semiconductor layers includedin the first through third mesas are exposed; oxidizing the III-Vsemiconductor layers of the first through third mesas from the sidesurfaces thereof; optically monitoring oxidized conditions on the III-Vsemiconductor layers of the second and third mesas and obtaining, fromtimes when the III-V semiconductor layers of the second and third mesasare terminated as well as the sizes thereof, an oxidization terminatingtime when oxidization of the III-V semiconductor layer of the first mesashould be terminated; and terminating oxidization of the III-Vsemiconductor layer of the first mesa to thus form a current confinementlayer including an aperture that is a non-oxidized region of the III-Vsemiconductor layer of the first mesa.
 8. The method as claimed in claim7, wherein the step of obtaining the oxidization terminating timecomprises the steps of: projecting light onto an area including thesecond and third mesas; and obtaining the oxidization terminating timewhen oxidization of the III-V semiconductor layer of the first mesashould be terminated on the basis of the times when the III-Vsemiconductor layers of the second and third mesas are totallyterminated and oxidization distances from the side surfaces of thesecond and third mesas.
 9. The method as claimed in claim 8, wherein thestep of obtaining the oxidization terminating time comprises the stepsof: calculating a rate of oxidization from the times when the III-Vsemiconductor layers of the second and third mesas are totallyterminated and the oxidization distances from the side surfaces of thesecond and third mesas; and obtaining the oxidization terminating timewhen oxidization of the III-V semiconductor layer of the first mesashould be terminated on the basis of the rate of oxidization.
 10. Themethod as claimed in claim 8, wherein: the oxidizable regions of theIII-V semiconductor layers containing Al in the second and third mesashave different sizes and are smaller than the oxidizable region of theIII-V semiconductor layer of the first mesa; and multiple pairs ofpatterns, each having the second and third mesas, are arranged withgiven periods so as to form a stripe pattern on the substrate.
 11. Themethod as claimed in claim 8, wherein the first mesa has a post shape.12. A method of fabricating a surface emitting semiconductor lasercomprising the steps of: forming, on a substrate, multiple monitor-usesemiconductor layers having stripes radiating from a center of thesubstrate, and a laser portion that includes semiconductor layers and islocated on the periphery of the multiple monitor-use semiconductorlayers; monitoring oxidized conditions on the multiple monitor-usesemiconductor layers when a selectively oxidized region is formed in thelaser portion; and controlling oxidization of the selectively oxidizedregion on the basis of the oxidized conditions thus monitored.
 13. Themethod as claimed in claim 12, wherein the stripes radiating from thecenter are arranged with rotational symmetry about the center.
 14. Themethod as claimed in claim 12, wherein the stripes radiating from thecenter are divided into multiple groups at a given center angle, andeach of the multiple groups has straight stripes.
 15. The method asclaimed in claim 14, wherein the stripes included in the adjacent groupsamong the multiple groups form an angle of approximately 45°.
 16. Amethod of fabricating a surface emitting semiconductor laser comprisingthe steps of: forming, on a substrate, multiple monitor-usesemiconductor layers having stripes radiating towards ends of thesubstrate, and a laser portion that includes semiconductor layers and islocated adjacent to the multiple monitor-use semiconductor layers;monitoring oxidized conditions on the multiple monitor-use semiconductorlayers when a selectively oxidized region is formed in the laserportion; and controlling oxidization of the selectively oxidized regionon the basis of the oxidized conditions thus monitored.
 17. The methodas claimed in claim 12, wherein the multiple monitor-use semiconductorlayers having two kinds of semiconductor layers having oxidizableregions of different sizes.
 18. The method as claimed in claim 12,further comprising a step of depositing resist on the substrate afteroxidization of the selectively oxidized region is terminated.
 19. Themethod as claimed in claim 12, wherein each of the laser portion and themultiple monitor-use semiconductor layers includes a first mirror layer,an active region formed thereon, a second mirror layer formed on theactive region, and a III-V semiconductor layer containing Al interposedbetween the first and second mirror layers, the III-V semiconductorlayer is selectively oxidized.
 20. A surface emitting semiconductorlaser comprising: a substrate; and a laminate of semiconductor layers onthe substrate, the semiconductor layers including a first reflectionmirror of a first conduction type, an active region on the firstreflector mirror, a current confinement region including an oxidizedregion, and a second reflection mirror of a second conduction type, amesa ranging at least from the second reflection mirror to the currentconfinement layer, the mesa extending at least from the secondreflection mirror to the current confinement layer, the oxidized regionof the current confinement layer utilizing an oxidization terminatingtime obtained by detecting times when oxidizable regions included in atleast two kinds of monitor-use semiconductor layers having differentshapes are totally oxidized.
 21. The surface emitting semiconductorlaser as claimed in claim 20, wherein the current confinement layer isan AlAs layer.
 22. The surface emitting semiconductor laser as claimedin claim 20, wherein the current confinement layer is an AlGaAs layer.23. An apparatus for fabricating a surface emitting semiconductor lasercomprising: a projection part projecting light onto an area including atleast two kinds of monitor-use mesas respectively including III-Vsemiconductor layers that contain Al and have side surfaces exposed,when the side surfaces and a side surface of a III-V semiconductor layerof a laser-use mesa that contains Al and a side surface exposed areoxidized; a photoelectric conversion part converting reflected lightsfrom the monitor-use mesas into electrical signals; an oxidizationterminating time estimation part that detects times when the III-Vsemiconductor layers of the two kinds of monitor-use mesas are totallyoxidized on the basis of the electrical signals, and estimates anoxidization terminating time when oxidization of the III-V semiconductorlayer of the laser-use mesa should be terminated; and an oxidizationcontrol part causing oxidization of the III-V semiconductor layer of thelaser-use mesa to be terminated at the oxidization terminating time tothus define a current confinement layer in the laser-use mesa.
 24. Theapparatus as claimed in claim 23, wherein the oxidization terminatingtime estimation part estimates an oxidization time corresponding to anoxidization distance to be formed in the laser-use mesa on the basis ofthe times when the III-V semiconductor layers of the two kinds ofmonitor-use mesas are totally oxidized and oxidization distancesthereof.
 25. The apparatus as claimed in claim 23, wherein theprojection part projects light onto multiple stripe patterns formed onthe substrate, in which each of the multiple stripe patterns is formedby the at least two kinds of monitor-use mesas.
 26. The apparatus asclaimed in claim 25, wherein the projection part projects light onto thearea including at least two kinds of monitor-use mesas radiating from acenter of the substrate.